The present paper deals with a disease of Bartlett pear trees which occurred in two orchards in the coastal region of central California (Contra Costa County). In one orchard the affected trees were scattered, somewhat in groups, over an area of several acres. The majority of these trees were not seriously injured. In the other orchard, several miles distant from the first one, most of the sick trees were severely injured, and occasionally one of them died during the period of observation in 1930 to 1934. The diseased trees were confined in this orchard to an area of about 20 to 25 acres. Insofar as the appearance and growth of the trees was concerned, there was a more or less sharp line of demarcation between the diseased and the healthy areas. Most of the trees in the diseased part of the orchard were suffering from the malady. The various treatments and analytical data concerning the affected trees to be discussed in the following sections refer to trees in the diseased area of this orchard. The disease was diagnosed b^ Smith and Thomas (8) as exanthema, and it will be referred to in this paper as such, although this does not imply that the disease is necessarily identical in its causes with other plant disorders designated by the same name.